This invention was made with government support under grants GM40553, GM07323, and GM15964 awarded by the National Institutes of Health and IBN-9317524 awarded by the National Science Foundation. The government has certain rights in the invention.
Gibberellins (GAs) are a major class of plant hormones controlling many developmental processes including seed development and germination, flower and fruit development, and flowering time. Gibberellins (GAs) play a role in a number of growth and developmental processes in plants. Severe GA-deficient mutants may exhibit reduced seed germination, dwarfism of virtually all organs, and aberrant flower, fruit and seed development. Although the GA biosynthetic pathway has been studied for some time little is known about GA perception or signal transduction.
Genetic analysis has uncovered two classes of mutants which are affected in their response to gibberellins. One class consists of dominant or semi-dominant mutants resembling gibberellin-deficient mutants but exhibiting reduced or no sensitivity to gibberellin. Mutants of this type have been isolated in maize, wheat and Arabidopsis thaliana (arabidopsis).
The second group, the "slender" mutants, have a recessive over-growth phenotype that is phenocopied by repeated treatments of wild type plants with gibberellin, and is consistent with a defect causing constitutive gibberellin response. These mutants have been studied in pea, tomato, barley and arabidopsis (Jacobsen, S. E. & Olszewski, N. E. (1993) The Plant Cell 5:887-896). Slender mutants in pea, tomato and barley contain lower endogenous levels of gibberellins than wild-type plants.
A slender phenotypic mutation in arabidopsis is termed the "spindly" or "spy" mutation. The spindly mutation is characterized by elongated petioles, yellow-green leaves, early flowering, long spindly bolts, partial male sterility and parthenocarpic fruit development. These phenotypes are also observed in wild type plants exhibiting a gibberellin overdose syndrome due to external applications of gibberellin (Jacobsen, et al. supra).
Spy phenotypic mutants were isolated from M.sub.2 populations of ethyl methylsulfonate (EMS)-mutagenized wild-type seeds by selection for germination in the presence of the gibberellin biosynthesis inhibitor, paclobutrazol (Jacobsen, et al. supra) . The phenotypes of the plants were typical of spy mutants and all of these phenotypes are observed, at some level, in wild type plants which have been repeatedly sprayed with GA.sub.3.
Growth retardants, typically in the form of sprays or washes are widely used, particularly in greenhouses to control plant growth. These chemicals act by reducing gibberellin levels of the plant. Direct treatment of plants with gibberellins or their analogs increase plant size over the entire treated area of the plant. While spindly and slender phenotypes have been described as early as 1922, the gene or genes associated with these phenotypes remain ellusive. Identification of the gene or genes associated with these phenotypes would permit gibberellin expression to be controlled without the need for chemical treatment. This will reduce chemical usage and minimize a potential environmental hazard.